EAS systems of the type described above, are, for example, disclosed and claimed in U.S. Pat. No. 3,665,449 (Elder and Wright). With such systems, a dual status marker of the type described above may be sensitized, i.e., the high-coercive force control elements thereof demagnetized, by applying an alternating, diminishing amplitude magnetic field, or by gradually removing an alternating field of constant intensity such as by withdrawing a bulk magnetic eraser of the type supplied by Nortronics Company, Inc. of Minneapolis, Minnesota. As disclosed in the U.S. Pat. No. 3,665,449 such a demagnetization operation may also be effected through the proper selection and arrangement of a series of permanent magnets in which adjacent magnets are oppositely polarized. By selecting the magnets to be of different strengths and by arranging them in an order ranging from highest to lowest (relative to the direction of travel), the magnetic field will appear to diminish in amplitude when passed over a control element. That patent also suggests that magnets of the same field strength may be arranged like inverted ascending steps or like an inclined plane so that the amplitude of the field is progressively diminished to produce the same result, and that it is not ordinarily necessary to demagnetize the control element in the strictest sense. Rather, the magnetic influence of the control element need only be reduced to an extent permitting magnetization reversal of the marker by the applied field.
While such techniques may be useful in many areas with the markers affixed to a wide variety of articles, the magnetic fields associated therewith have been found to unacceptably interfere with magnetic states associated with certain articles, such as prerecorded magnetic video and audio cassettes utilized in video rental businesses. Because of the compact size and popularity of such prerecorded magnetic cassettes, they are frequent targets for shoplifters, and hence likely articles with which anti-theft markers would be used. At the same time however, such affixed markers would be desirably sensitized upon return of the article, and it has been found that prior art demagnetization apparatus such as those described above may unacceptably affect signals prerecorded on the magnetic tapes within the cassettes.